1. Field of the Invention
This invention pertains to nonwoven webs formed by extruding filaments of thermoplastic polymers and collecting them into a sheet which is then bonded to provide strength and structural integrity. While such webs are currently available, they tend to be stiff and paper-like when compared to woven textiles of similar basis weight. Particularly in applications where the material is to be placed in contact with a person's skin such as disposable diapers and catamenial devices, for example, this stiff paper-like feeling is perceived as a disadvantage. A number of attempts have been made to soften the nonwoven webs as formed by chemical or physical treatment. However, such attempts have not been entirely satisfactory due to the added cost involved or the resulting adverse effect on other web properties.
Accordingly, it is desired to economically produce a soft, nonwoven web without deleterious side effects. The present invention is directed to such a method.
2. Description of the Prior Art
U.S. Pat. No. 3,692,618 issued Sept. 19, 1972 to Dorschner et al. describes a process for forming continuous filament nonwoven webs. In this process a number of continuous filaments of a synthetic polymer such as polypropylene are simultaneously spun and gathered into a straight row of side-by-side untwisted bundles. These bundles are drawn downwardly at a high velocity in an individual surrounding gas column and directed to impinge on a carrier belt moving so that the bundles extend in a straight row across the carrier at an angle to the direction of its movement. As the bundles impinge against the carrier they are divided and deposited in a loop-like arrangement extending back and forth across the direction of travel of the carrier to form a web which is characterized by a multiple number of side-by-side lengthwise sections.
U.S. Pat. No. 3,855,046 issued Dec. 17, l974 to Hansen et al. describes bonding of nonwoven webs of the type produced according to the Dorschner et al. patent. In accordance with the Hansen et al. method webs having releasable bonds are formed by passing the web through a nip formed by an anvil roll and a roll having a plurality of raised points in a pattern selected to yield the web with adequate integrity and tensile strength.
U.S. Pat. No. 3,855,045 issued Dec. 17, 1974 to Brock describes a further bonding embodiment wherein the resulting web has self-sizing characteristics. Such webs are generally of heavier basis weight in the range of 1-3 ounces per square yard and are characterized by primary bonds in discrete compact areas and secondary bonds in the remaining surface. The secondary bonds provide stiffness and strength required for web processing in applications such as the manufacture of bed linens, garments, drapery materials, etc. Upon washing, however, the secondary bonds are disrupted producing increased softness and improved tactile properties such as hand, drape and the like.
U.S. Pat. No. 3,870,567 issued Mar. 11, 1975 to Palmer et al. is directed to a battery separator produced from nonwoven microfiber mats made wettable through the incorporation of an internal wetting agent which tends to bloom under conditions of use. The preferred wetting agents have an HLB (hydrophilic lypophilic balance) less than 5. However, an additional wetting agent having a higher HLB number can be incorporated to provide a higher degree of wetting.